1. Field Of The Invention
This invention relates to improvements in amplifier circuits, and more particularly to improvements in amplifier biasing methods and circuits, and still more particularly to improvements in dynamic biasing methods and circuits for class A amplifiers.
2. Description Of The Prior Art
Operational amplifiers often find use in circuits in which they are required to provide an output which has the capability of sourcing and sinking current to and from an associated load. In typical integrated circuit processes, sourcing current can be accomplished simply, since an NPN transistor can be used for a source transistor. However, sinking current from the load requires special design considerations. One circuit which is widely used to fulfill both sourcing and sinking requirements has a symmetrical output amplifier comprising both NPN and PNP transistors with the collector-emitter path of the NPN transistor being connected between the supply voltage source and the output, and with the collector-emitter path of the PNP transistor connected between the output and a reference potential, or ground. Such circuit structure, however, loses the advantages accompanying NPN transistor circuits, and, moreover, often require special offset compensation design. Furthermore, the design of the required PNP transistor devices is significantly more complicated in device fabrication than would be a corresponding NPN transistor device for the same or similar circuit considerations.